A final serious abnormality of the cardiac rhythmicity-conduction system is cardiac arrest. This results from cessation of all electrical control signals in the heart. That is, no spontaneous rhythm remains.
Cardiac arrest is especially likely to occur during deepanesthesia, when many patients develop severe hypoxiabecause of inadequate respiration. The hypoxia pre-vents the muscle fibers and conductive fibers from main-taining normal electrolyte concentration differentials across their membranes, and their excitability may be so affected that the automatic rhythmicity disappears.
In most instances of cardiac arrest from anesthesia, prolonged cardiopulmonary resuscitation (many minutes or even hours) is quite successful in re-establishing a normal heart rhythm. In some patients, severe myocardial disease can cause permanent or semipermanent cardiac arrest, which can cause death. To treat the condition, rhythmical electrical impulses from an implanted electronic cardiac pacemaker have been used successfully to keep patients alive for months to years.